In recent years, in order to enhance portability of portable information processors such as notebook-size computers, there have been made advances in production of thinner and lighter design of the processors themselves and also of thinner enclosures forming outer cases of the processors. Meanwhile, the enclosure is being made of a metallic material for improvement of its mechanical strength, for electromagnetic shielding, and for radiation of heat developed inside the apparatus.
A conventional portable information processor will be described below with reference to the accompanying drawings.
FIGS. 2A and 2B show external views in perspective of the conventional portable information processor, FIG. 2A shows its state having a display portion opened and FIG. 2B shows its state having the display portion closed. FIG. 3 is a sectional view of the display portion. In the drawings, display portion 22 is joined to body portion 21 of the portable information processor by a hinge assembly (not shown) for opening and closing. Display portion 22 has a liquid crystal display unit 25 disposed between back enclosure 23 and front enclosure 24. Back enclosure 23 is formed of a metallic material such as aluminum for improvement of the mechanical strength, electromagnetic shielding, and radiation of heat generated inside the apparatus. For weight reduction, especially in recent years, use of magnesium alloy having smaller specific gravity and greater strength than aluminum has come to be more prevalent. In addition, the enclosure is formed so as to have the thinnest possible wall thickness.
Portable information processors in general, as they are called “note” or “book”, are shaped in a flat and low box form having a virtually rectangular flat portion so that they may be easily put in a brief case or the like. There are one type having the display portion and the body portion joined together via a hinge assembly as shown in FIG. 2A and another type in which the liquid crystal display unit is built into the body portion.
In recent years, the technology of producing thinner and lighter portable information processor has made progress and accordingly the chances are increasing of the processors being carried around by being put in a brief case or the like. However, in a case where the user carrying the processor gets on a crowded train, for example, the brief case receives a high pressure from outside. At this time, external force F as shown in FIG. 3 is applied to display portion 22. This external force F causes deformation in thin-walled back enclosure 23 and produces such a trouble as breakage of liquid crystal display unit 25 housed therein. To prevent this, such methods as to increase the basic wall thickness of the enclosure or to dispose a number of ribs (protrusions) on the interior of the enclosure are considered. However, when these measures are taken, the portable information processors are prevented from being thin-walled and light-weighed and, hence, their portability is impaired. Further, when a number of ribs are provided, cavitations occur in the molding process of the enclosure at the portions where the shape is uneven. As a result, such problems as formation of molten-metal wrinkles or cracks arise, which not only greatly reduces the yields but also leads to increase in weight of the enclosure. Accordingly, approximately 1 mm is considered to be the smallest possible basic wall thickness of the enclosure of conventional portable information processors.